Allosteric regulation of aspartate transcarbamoylase. Effect of active site ligands on the reactivity of sulfhydryl groups of the regulatory subunits

Biochemistry ◽  
1977 ◽  
Vol 16 (23) ◽  
pp. 5084-5091 ◽  
Author(s):  
Michael N. Blackburn ◽  
H. K. Schachman
Keyword(s):  
Active Site ◽  
Allosteric Regulation ◽  
Sulfhydryl Groups ◽  
Aspartate Transcarbamoylase ◽  
Regulatory Subunits

Allosteric theory

Hemoglobin ◽  
2018 ◽  
pp. 42-57
Author(s):  
Jay F. Storz
Keyword(s):  
Active Site ◽  
Binding Sites ◽  
Allosteric Regulation ◽  
Theoretical Models ◽  
State Model ◽  
Regulatory Control ◽  
Indirect Interaction ◽  
Protein Activity ◽  
Conformational States ◽  
Two State Model

Chapter 3 provides a brief overview of allostery, the modulation of protein activity that is caused by an indirect interaction between structurally remote binding sites. In this mode of intramolecular regulatory control, the binding of ligand at a protein’s active site is influenced by the binding of another ligand at a different site in the same protein. This interaction at a distance is mediated by a ligation-induced transition between alternative conformational states. Hemoglobin is regarded as the “allosteric paradigm,” and the oxygenation-linked transition between alternative quaternary conformations provides a textbook example of how allostery works. This chapter reviews different theoretical models, such as the Monod-Wyman-Changeux “two-state” model, to explain the allosteric regulation of hemoglobin function.

scholarly journals Ligand interactions at the active site of aspartate transcarbamoylase from Escherichia coli

Biochemistry ◽  
1986 ◽  
Vol 25 (7) ◽  
pp. 1605-1611 ◽  
Author(s):  
Paul R. Dennis ◽  
M. Vijaya Krishna ◽  
Maria Di Gregorio ◽  
William W. C. Chan
Keyword(s):  
Escherichia Coli ◽  
Active Site ◽  
Aspartate Transcarbamoylase ◽  
Ligand Interactions

scholarly journals Conformational Plasticity of the Active Site Entrance in E. coli Aspartate Transcarbamoylase and Its Implication in Feedback Regulation

2020 ◽  
Vol 21 (1) ◽  
pp. 320
Author(s):  
Zhen Lei ◽  
Nan Wang ◽  
Hongwei Tan ◽  
Jimin Zheng ◽  
Zongchao Jia
Keyword(s):  
Active Site ◽  
Feedback Regulation ◽  
Aspartate Transcarbamoylase ◽  
Regulatory Subunit ◽  
Dynamic Simulations ◽  
E Coli ◽  
Open Conformation ◽  
Conformational Plasticity ◽  
The Stability ◽  
Remote Feedback

Aspartate transcarbamoylase (ATCase) has been studied for decades and Escherichia coli ATCase is referred as a “textbook example” for both feedback regulation and cooperativity. However, several critical questions about the catalytic and regulatory mechanisms of E. coli ATCase remain unanswered, especially about its remote feedback regulation. Herein, we determined a structure of E. coli ATCase in which a key residue located (Arg167) at the entrance of the active site adopted an uncommon open conformation, representing the first wild-type apo-form E. coli ATCase holoenzyme that features this state. Based on the structure and our results of enzymatic characterization, as well as molecular dynamic simulations, we provide new insights into the feedback regulation of E. coli ATCase. We speculate that the binding of pyrimidines or purines would affect the hydrogen bond network at the interface of the catalytic and regulatory subunit, which would further influence the stability of the open conformation of Arg167 and the enzymatic activity of ATCase. Our results not only revealed the importance of the previously unappreciated open conformation of Arg167 in the active site, but also helped to provide rationalization for the mechanism of the remote feedback regulation of ATCase.

Further studies on aspartate transcarbamoylase: molecular weight of the c3r6 complex and analysis of succinate inhibition in the native enzyme

1976 ◽  
Vol 54 (12) ◽  
pp. 1061-1068
Author(s):  
William W.-C. Chan
Keyword(s):  
Molecular Weight ◽  
Competitive Inhibition ◽  
Gel Filtration ◽  
Frictional Coefficient ◽  
Sedimentation Coefficient ◽  
Native Enzyme ◽  
Aspartate Transcarbamoylase ◽  
Unusual Structure ◽  
Regulatory Subunits ◽  
Method Of Calculation

The complex which is formed when excess regulatory subunits (r2) of aspartate transcarbamoylase (EC 2.1.3.2) are added to a dilute solution of the catalytic subunit (c3) has been studied by gel-filtration on Sephadex G-200. The elution volume indicates a Stokes' radius of between 5.42 and 5.92 nm, depending on the method of calculation. Using the sedimentation coefficient of 7.7 S previously determined, the molecular weight is estimated to be close to 200 000, in support of the c3r6 structure proposed earlier for the complex. The calculated frictional coefficient indicates abnormal hydrodynamic properties which are probably due to unusual structure characteristics.The pattern of succinate inhibition of native aspartate transcarbamoylase has also been analyzed. At low concentrations, succinate activates the enzyme, presumably by converting it from the taut state to the relaxed (R) state. Further increase in the succinate concentration leads to competitive inhibition of the R state. Using a novel procedure for analysis of the data, the Michaelis constant for aspartate of the R state has been estimated to be about 7 mM. This value is close to the Km of c3r6 for aspartate, measured under identical conditions. The result therefore provides further evidence suggesting that the c3r6 complex resembles the R state of the native enzyme.

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